1. Field of the Invention
The subject of the invention is the conversion method of T8 type Polyhedral Oligomeric Silsesquioxanes (POSS) to T10 type compounds using acidic catalyst.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Most Polyhedral (multiwalled) Oligomeric Silsesquioxanes (POSS) are specific example of silsesquioxanes (SQ) which are described by the specific formula (RSiO1,5)n, wherein R symbol indicate hydrogen atom, alkyl group, aryl group, halogen, alkenyl group and derivatives thereof, usually n have a value: 6, 8, 10, 12. SQ is most frequently prepared by hydrolysis and subsequent condensation of trifunctional silanes in slightly elevated or room temperature in and using basic and acidic catalyst. As a precursor for SQ synthesis specific silanes RSiX3 (X=Cl, OR, OAc, NH2 and other) are used which are easy to hydrolyse giving silanol groups and are further subjected to polycondensation. Hydrolysis speed depends on the type of substituent on silica atom which are not hydrolysed (bigger substituent, lower speed) and type of X function group. Besides, temperature, monomer concentration, amount of water added, type of solvent and catalyst are also influencing the efficiency. Polycondensation performed in such manner gives various structures of silsesquioxanes as presented on FIG. 1.
Apart from SQ presented above, POSS in small amounts are also generated during hydrolytic polycondensation reaction. Cage-formed and constructed from complete multiple one-and-half silicate RSiO1,5 units SQ are also included. POSS are signed with Tn symbol, wherein usually n have a 6, 8, 10, 12 value and indicate amount of silica atoms present in the corner of polyhedron.
Polyhedral oligomeric silsesquioxanes are prepared in general from organic trichloro- or trialkoxysilanes in hydrolytic polycondensation process described above. Most commonly used catalyst of this reaction are non-organic acid such as e.g. HCl, H2SO4 or bases (organic amines, metal hydroxides). It is necessary to use moderate amounts of water (most preferably in molar H2O/RSiX3 ratio=1:1) in order to maintain heterofunctional condensation instead of competitive homocondensation of silanols.
Typical POSS structures are presented on FIG. 2.
Most commonly found are type T8 compounds due to presence of four interconnected Si4O4 with high rings stability which compose core of the cage. Generation of less thermodynamically unstable POSS such as T10 or T12 is a result of spontaneous conversion of T8 type POSS. In general, they are produced with low efficiency as a by-products in reaction of POSS arms modification. Such T8 cage modification into the bigger one was published by several research groups [(a) Y. Kawakami, K. Yamaguchi, T. Yokozawa, T. Serizawa, M. Hasegawa, Y. Kabe, Chem. Lett. 2007, 36, 792; (b) A. R. Bassindale, Z. Liu, I. A. Mackinnon, P. G. Taylor, Y. Yang, M. E. 100 Light, P. N. Horton, M. B. Hursthouse, Dalton Trans. 2003, 2945. (c) V. Ervithayasuporn, X. Wang, Y. Kawakami, Chem. Commun. 2009, 5130].
Nevertheless, these compounds most commonly were not isolated in a pure form. It is directly connected to the similarity in solubility for compounds of T8, T10, T12 type and higher. Separation of POSS is particularly difficult when compounds, e.g. T10 and T12, exhibit similar physico-chemical properties.
Kawakami et al. described generation of POSS T8, T10 and T12 during hydrolysis of 4-substituted phenyltriethoxysilan in presence of TBAF (tetrabutylammonium fluoride). Separation of POSS with different cage size is conducted by crystallization using different type of solvent solutions e.g. acetonitrile/THF (v/v, 1:1), pure hexane or ethanol/hexane mixtures (v/v, 1:4). Known ways to obtain T10 and T12 cages are presented in Table 1 based on publication: Lickiss, P. D.; Rataboul, F. Fully Condensed Polyhedral Oligosilsesquioxanes (POSS): From Synthesis to Application. Adv. Organomet. Chem. 2008, 57, 1-116.
TABLE 1Examples of reaction conditions to obtain different T8 or T12 type silsesquioxanes.The valueof thechemicalCageType of RStarting compound Efficiency shift 29Sisizesubstituentand reaction conditions[%]NMRT10—HHSiCl3 + c-C6H12/PhMe +3.6−86.25H2SO4—CpCpSiCl3 + H2O, 67−71.50THF + (NH4)2CO3, 7 days—CH═CH2[CH2═CHSi(OEt)2]2O + 26−81.48H2O, TBF, THF/CH2Cl2, 2 days—C6H5PhSiCl3 + H2O, toluene, ——KOH, 9 h, subsequently re-crystallization from benzene/n-hexane mixtureT12—HHSiCl3 + H2O, H2SO4,3.5−85.78, cyclohexane/toluene, 6 h−87.76—CH═CH2[CH2═CHSi(OEt)2]2O + H2O, 15−81.34, TBF, THF/CH2Cl2, 2 days−83.35—C6H5PhSiCl3 + H2O, KOH, THF, ——reflux, 3 days
Besides above methods there is a method know in the literature for obtaining T10 type cages by conversion of SQ using fluoride ions. Rikowski et al. found that T10 and T12 POSSs are generated as a result of T8 cage conversion using NaF and 18-crown-6 as a catalyst. This conversion has given following efficiencies: 28% T8, 61% T10 and 11% T12.
Surprisingly, it has been discovered that usage of organic acid in form of triflic acid as a catalyst in conversion process of polyhedral oligomeric silsesquioxane constructed as a closed cage consisting of eight RSiO1.5 units (T8 cage; [RSiO1.5]8) into the cage made of ten RSiO1.5 units (T10 cage; [RSiO1.5]8) enabled obtaining high efficiency of the process and isolation of crude reaction products in pure form.